Graphite-based heat sinks and method and apparatus for the manufacture thereof

ABSTRACT

One embodiment of a heat sink comprises a metal support member having a groove disposed at a surface thereof and a fin disposed at the groove. The fin comprises a graphite-based material having a metal-based coating disposed thereon, and the fin is retained at the groove via a soldered joint at the metal-based coating and the groove. Another exemplary embodiment of a heat sink comprises a plurality of fins alternatingly arranged with a plurality of spacers. A method of fabricating a heat sink comprises preparing a surface of a graphite-based substrate, removing particulate matter generated from the preparation of the surface of the substrate, applying a metal-based coating at the surface of the substrate, and arranging the substrate to form a heat sink structure. An apparatus for cladding fins of a heat sink with a protective material comprises a first chamber that facilitates the preparation of substrate surfaces, a grit-removing apparatus disposed adjacent to the first chamber, a second chamber that facilitates the application of the protective material to the substrate surfaces, and a transport device configured to facilitate the movement of the substrates through the first chamber, to the grit-removing apparatus, and through the second chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/340,445 filed Jan. 10, 2003, the contents of which are incorporatedby reference herein in their entirety.

BACKGROUND

This disclosure relates generally to heat sinks and, more particularly,to graphite-based heat sinks and a method and an apparatus for themanufacture thereof.

Heat sinks are generally utilized to provide for the conductive transferof heat from a heat source (e.g., an electronic component) to asurrounding environment. The conductive transfer of heat from the heatsource is most efficient when the heat sink is fabricated from amaterial having a high coefficient of thermal conductivity to facilitatethe rapid conduction of heat from the heat source and its dissipation tothe surrounding environment. Such materials include metals such ascopper, aluminum, tungsten, molybdenum, alloys of the foregoing metals,and the like. Heat sinks fabricated from such metals and alloys,however, while providing adequate heat transfer capabilities, typicallyadd significant cost and weight to the systems into which they areincorporated.

To alleviate problems associated with weight, the fins of the heat sinksmay be made of lighter materials having comparable or improved heattransfer properties. One example of such a material is high conductivitygraphite, which may be utilized in a pure form or may be combined withanother material to form a graphite composite. However, difficultiesassociated with the attachment of graphite or graphite composite heatsink fins pose significant obstacles to the use of such materials. Inparticular, because graphite is not solderable, attachment of graphitefins to a metal base are oftentimes made by alternate means, e.g., withadhesives such as epoxies. Furthermore, because graphite is by nature abrittle material, heat sink fins fabricated from graphite or graphitecomposites typically crack, chip, or flake, thereby potentiallycompromising the integrity of the heat sink structure. Chipping orflaking of the graphite or graphite composite material may further raiseissues with respect to the contamination of the componentry of thedevice at which the heat sink is disposed. In particular, chipping orflaking of the graphite materials may contaminate and detrimentallyaffect the operation of electronic components from which heat must beremoved to ensure the proper operation of an electronic system.

SUMMARY

Disclosed herein are heat sinks, a method for fabricating a heat sink,and an apparatus for cladding fins of a heat sink with protectivematerial. One exemplary embodiment of a heat sink comprises a metalsupport member having a groove disposed at a surface thereof and a findisposed at the groove. The fin comprises a graphite-based materialhaving a metal-based coating disposed thereon, and the fin is retainedat the groove via a soldered joint at the metal-based coating and thegroove. Another exemplary embodiment of a heat sink comprises aplurality of fins alternatingly arranged with a plurality of spacers,the fins comprising a graphite-based material having a metal-basedcoating disposed thereon, and the spacers comprising either metal orgraphite-epoxy coated with metal.

A method of fabricating a heat sink comprises preparing a surface of agraphite-based substrate, removing particulate matter generated from thepreparation of the surface of the substrate, applying a metal-basedcoating at the surface of the prepared substrate, and arranging theprepared substrate having the metal-based coating to form a heat sinkstructure.

An apparatus for cladding fins of a heat sink with a protective materialcomprises a first chamber configured to facilitate the preparation ofsubstrate surfaces of the fins of the heat sink, a grit-removingapparatus disposed adjacent to the first chamber, a second chamberdisposed adjacent to the grit-removing apparatus and being configured tofacilitate the application of the protective material to the substratesurfaces of the fins, and a transport device configured to facilitatethe movement of the substrate surfaces through the first chamber, to thegrit-removing apparatus, and through the second chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the exemplary drawings, wherein like elements are numberedalike in the several figures:

FIG. 1 is a cross-sectional representation of a heat sink havinggraphite-epoxy fins clad with a metal coating disposed in grooves of ametal support;

FIG. 2 is a cross-sectional representation of a heat sink havinggraphite-epoxy fins alternately arranged with spacers;

FIG. 3 is a plan view of a heat sink fin having a metal coating;

FIG. 4 is a perspective view of a fin of a heat sink in which aprotective coating can be selectively applied using a mask;

FIG. 5 is a schematic representation of an apparatus by which the finsof the heat sink of FIG. 1 may be coated; and

FIG. 6 is a cross-sectional representation of a heat sink havinggraphite-epoxy fins clad with protective coatings disposed atline-of-sight surfaces.

DETAILED DESCRIPTION

Disclosed herein are heat sinks having graphite-based fins. In oneexemplary embodiment, a heat sink is defined by fins mounted withingrooves disposed in a support surface. In another exemplary embodiment,a heat sink is defined by an alternating arrangement of fins andspacers. Also disclosed are methods of fabricating heat sinks bymetallizing graphite-based substrates and either disposing thesubstrates as fins at a support or arranging the substrates withspacers. Exemplary materials that may be used for the metallizinginclude, but are not limited to, metals, alloys, metal-based compositematerials, refractory materials, and the like. The metallizing of thesubstrates to form fins preferably provides a surface finish thatfacilitates the connection (e.g., the soldering) of the fins to thesupport. The metallizing also increases the robustness of the fins andfurther serves to form a protective coating that inhibits chippingand/or flaking of the graphite material, which may detrimentally affectthe performance of the heat sink or the components associated therewith.

Referring to FIG. 1, a heat sink is shown generally at 10. Heat sink 10comprises a support 12 and a plurality of fins 14 extending from support12. Fins 14 are preferably disposed in grooves disposed within support12 and secured therein. Alternately, as is shown in FIG. 2, a heat sink110 may comprise an arrangement of alternatingly-positioned fins 114 andspacers 115 to form a heat sink structure. The fins 114 and spacers 115are preferably fixed in a parallel-planar relationship by any suitablemeans, e.g., a solder joint 117. In either configuration, the heat sinkis generally configured to be attached to a, heat generating electricaldevice, e.g., a microchip module or a similar device.

Referring back to FIG. 1, the graphite-based fins 14 preferably comprisegraphite or a graphite-epoxy composite (hereinafter “graphite”)substrates clad with a metal (“metallized”) to facilitate the securingof fins 14 within the grooves of support 12 and to inhibit the flakingor chipping of the graphite material. The foot portion of each fin 14 ispreferably securely disposed at support 12 via a solder joint 17,although any suitable method of attachment such as ultrasonic welding,brazing, or the like may be utilized. Fins 14 are also planar instructure such that the facial areas of each fin 14 are maximized inorder to effect a maximum amount of heat transfer from each fin 14 tothe adjacent environment. The planar facial areas of each fin 14 may beof any configuration including, but not limited to, round, elliptical,angular, or any combination of the foregoing configurations.

Referring now to FIG. 3, one exemplary embodiment of a metallized heatsink fin is shown at 14. The underlying structure of each fin 14comprises the substrate 16 fabricated of the graphite. Substrate 16 ispreferably substantially uniformly coated with the coating, shown at 18,thereby cladding the exposed surfaces. A substantially uniform coatingis one in which variations in thickness of the coating over the area ofthe substrate to which the coating is applied are functions of theconditions under which the coating is applied (e.g., temperature,rheological characteristics of the coating material, method ofapplication of the coating material, and the like). As is shown, boththe facial surfaces as well as the edges of substrate 16 are coated to athickness L of about 25 micrometers (um) to about 50 um. The edges maybe defined by a radius r at the edges of substrate 16, which may beformed during the application of coating 18 as a result of the flowcharacteristics of the metal during its application.

As stated above, coating 18 is selected and disposed at the exposedsurface of substrate 16 to allow for the soldering attachment of fins tosupport 12 (or to spacers) as well as to prevent damage to fins 14 andfurther to inhibit the flaking or chipping of the graphite material. Thegraphite from which substrate 16 is fabricated may allow the coatingmaterial to penetrate the surface of substrate 16 to a substantialdegree, thereby securely cladding substrate 16. Coating 18 preferablycomprises a lightweight metal having a high coefficient of thermaltransfer and having corrosion inhibitive- or preventive properties andsufficient durability when applied to substrate 16 such that damage tofins 14 during handling of the heat sink is avoided or at leastminimized. Metals that may be used include, but are not limited to,aluminum, zinc, copper, silver, nickel, alloys of the foregoing metals,high temperature refractory coatings, combinations of the foregoingmaterials, and the like. A preferred coating material comprises about85% zinc and about 15% aluminum. A more preferred coating comprises pureor near-pure zinc.

Referring now to both FIGS. 1 and 3, fins 14 are typically prepared andcoated prior to assembly of heat sink 10. In one exemplary embodiment,the cladding of fins 14 comprises the preparation of substrate 16 andthe application of coating 18 to substrate 16 to form fins 14 prior tothe mounting of fins 14 at support 12. The preparation of substrate 16typically comprises abrading the substrate surface. One method ofabrading the substrate surface comprises a sand-blasting orgrit-blasting process, which increases the area of the substrate surfaceand creates an anchor profile on the surface to enhance the adhesion ofthe protective coating to the graphite. The preparation of substrate 16may further comprise removing the particulate matter resulting from thesand-blasting or grit-blasting process. Abrading the substrate surfacemay further provide for the cleaning of the surface (e.g., the removalof foreign particulate material and minor imperfections embedded in thesurface layers of the material). The preparation of the substratesurface may be effected by other methods such as, for example, reactiveion etching in which chemically active ions are accelerated along thelines of a generated electromagnetic field to bombard the substratesurface perpendicular to the plane in which the surface extends, therebyremoving the surface layer.

The application of coating 18 to substrate 16 typically comprises thespray deposition of the metal, alloy, or refractory material onto theprepared surface of substrate 16. Preferably, the coating is applied tothe surface of substrate 16 utilizing an arc spray technique. In the arcspray technique, an arc is struck between two wire electrodes fabricatedof the metal to be deposited, and the electrodes are melted by the heatgenerated from the arc. As the electrodes are melted, a pressurized gasis directed at the electrodes, and the molten metal droplets areprojected at substrate 16 and impinged on the substrate surface at highvelocity. In another method of the application of coating 18 known asthe flame spray technique, the metal is melted via a flame generatedfrom a combustible gas, and the molten metal droplets are projected ontoa heated substrate 16. Other techniques by which coating 18 may bedisposed on substrate include, but are not limited to, vapor deposition.

The coating may be selectively applied by masking areas of substrates16. In one embodiment as is shown with reference to FIG. 4, a maskingmaterial 40 is applied to some areas of substrate 16 to allow substrate16 to be metallized solely at the non-masked areas 42. Coating materialapplied to some surfaces (particularly to the surfaces at which the finsare joined to the body to form the heat sink) facilitates theeffectiveness of the soldered joints by which the fins are easily andreadily attached to the body while allowing the weight of the fin to bekept to a minimum. Thus, masking material 40 allows the heat transfersurfaces to remain free of the coating. In other embodiments, becausechipping and flaking of the composite material generally occurs at thecorners and edges of substrate 16, masking material 40 may also beapplied to the facial areas of substrate 16 in order to avoid theunnecessary disposing of excess coating material on substrate 16,further limiting the amount of coating material unnecessarily disposedon substrate 16.

Referring now to FIG. 5, the apparatus by which-substrates 16 are cladwith the protective material is shown generally at 20. Apparatus 20allows for the preparation of the surfaces of substrates 16 and theapplication of the coating material in an assembly line format to formfins 14, which may be assembled with supports to form heat sinks.Apparatus 20 comprises a first chamber 22, a second chamber 24, and atransport device 26 by which substrates 16 can be transported throughchambers 22, 24 for preparation and application of the coating. Agrit-removing apparatus 23 is preferably disposed intermediate chambers22, 24 to remove residue and particulate matter generated in theabrading process. The transport of substrates 16 through apparatus 20 ispreferably automated and controlled via a control system (not shown)disposed in communication with apparatus 20.

First chamber 22 is preferably an area in which the surfaces ofsubstrates 16 may be prepared for the subsequent application of theprotective material to form the coating. As stated above, thepreparation of substrates 16 typically comprises an abrasive treatmentof the surfaces of substrates 16. Such an abrasive treatment is effectedvia the mechanical operation of a suitable treatment device 28, e.g., asand-blasting or grit-blasting device or a reactive ion etching device.

Grit-removing apparatus 23 preferably comprises a jet of inert gasdirected at the surfaces of fins 14. Other apparatuses similarlyoperated, e.g., solvent or aqueous sprayers optionally followed by blowdry streams, may alternately provide for the removal of grit generatedin the abrading process.

Second chamber 24 is an area in which the protective coatings aredisposed at the prepared substrates 16. Preferably, second chamber 24 isdisposed adjacent to grit-removing apparatus 23 such that a continuousfeed of substrates 16 can be maintained through apparatus 20. As statedabove, the application of the protective coating is effected via theoperation of a spray device 30, which is preferably an arc spray device.

Transport device 26 provides for the assembly line treatment ofsubstrates 16 to form fins 14 that may be assembled to form the heatsinks. The assembly line treatment is effected by the movement of theworkpiece substrates 16 through chambers 22, 24 in the direction of anarrow 32. Movement of substrates 16 may be either continual orcontinuous; in either case, however, the movement is preferablyautomated such that operator intervention is minimal and controlled suchthat the level of skill required to operate apparatus 20 is low.Transport device 26 may be a conveyor belt, as is shown. Other devicesthat may provide for the transport of substrates through the chambersinclude, but are not limited to, carousels, trolleys, and the like. Theproduct fins 14 are removed from transport device 26 preferablysubsequent to their exiting from second chamber 24.

Another exemplary embodiment of cladding fins 14 comprises preparingonly the surfaces of the fins at which contact is made during thehandling or assembly of the heat sink and applying the protectivematerial only to those surfaces. Handling surfaces are typically theline-of-sight surfaces that comprise the outer edges of the fins as wellas the facial surfaces of the fins disposed at the ends of a heat sink.Handling surfaces may, however, comprise the surfaces of the finsintermediate the edges.

Referring now to FIG. 6, heat sink 10 on which only the line-of-sightsurfaces are coated is shown. In such an embodiment, heat sink 10 isfully assembled by disposing the graphite fins 14 at the grooves ofsupport 12 by any suitable means prior to coating. Cladding of theline-of-sight surfaces, particularly those surfaces at the edges of thefins and at which contact is made during the handling or assembly ofheat sink 10, provides a protective coating to inhibit the chippingand/or flaking of the graphite-epoxy composite material while surfaces36 at which contact is less likely to be made remain uncoated orminimally coated. As described above, application of coating 18 to theline-of-sight surface enhances the robustness of the assembled heat sink10. The line-of-sight surfaces of the assembled heat sink 10 may beprepared and coated using techniques similar to those described above.

While the invention has been described with reference to an exemplaryembodiment, it will be understood by those of skill in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. An apparatus for cladding fins of a heat sink with a protectivematerial, said apparatus comprising: a first chamber configured tofacilitate the preparation of substrate surfaces of said fins of saidheat sink; a grit-removing apparatus disposed adjacent to said firstchamber; a second chamber disposed adjacent to said grit-removingapparatus and being configured to facilitate the application of saidprotective material to said substrate surfaces of said fins; and atransport device configured to facilitate the movement of said substratesurfaces through said first chamber, to said grit-removing apparatus,and through said second chamber.
 2. The apparatus of claim 1, whereinsaid first chamber comprises an abrasive treatment device.
 3. Theapparatus of claim 2, wherein said abrasive treatment device comprises agrit-blasting device.
 4. The apparatus of claim 1, wherein said secondchamber comprises a spray device.
 5. The apparatus of claim 4, whereinsaid spray device is selected from the group of spray devices consistingof arc spray devices, thermal spray devices, and vapor depositiondevices.
 6. The apparatus of claim 1, wherein said transport device is aconveyor belt.